A head presently in use measuring the jacket thickness of an electric cable uses an inductive probe which follows the indulations of the cable surface as the cable moves continuously past the head. The head maintains a predetermined orientation and, if moved, returns to the same position. Examples of such a head are disclosed in U.S. Pat. No. 4,051,430 issued Sept. 27, 1977 to Louis G. Miliette et al and U.S. Pat. No. 4,064,634 issued Dec. 27, 1977 to Dan B. Davis, both assigned to Northern Telecom Limited.
On disadvantage of the above-mentioned head is that it does not accommodate a rapid increase in cable diameter such as that produced by a bulge in the cable jacket. Also, the complexity of the supporting mechanism makes it difficult to maintain in operational condition. Other disadvantages are that variable pressure of the device may cause scoring the cable jacket and vibration may result in incorrect measurements.